Searches for lepton flavour violation in the tau -> 3mu decay with the ATLAS Experiment

味道不是一个基本的对称性，我们知道它是违反标准模型（SM），无论是在中微子和夸克部门，通过混合。因此，期望带电轻子味违反（cLFV）是很自然的，但是，尽管g-2实验和B工厂暗示了味异常，但它从未在自然界中被观察到，它的观察将是超越SM物理学的明确证据。虽然严格的限制已被设置在electronand μ子通道，在tau的情况下的约束要弱得多。辛辛纽物理学很可能与更重的τ星产生更强的耦合，这使它成为理想的搜索地点。该项目将使用完整的运行2和部分运行3 ATLAS数据，使用金τ-> 3 μ子通道，以其干净的最终状态搜索LFV τ衰变。学生将首先分析在重味衰变中产生的tau，开发估计背景的方法和提取信号的多变量技术。在此基础上，将工作推广到W玻色子衰变中产生的τ，并将两个搜索结果结合起来。总之，这些都有可能提供超出当前限制的灵敏度，如果没有观察到新的物理现象，则对LFV τ衰变设置最严格的限制。该小组以前在W玻色子测量和tau最终状态的搜索方面都有广泛的经验。

Flavour is not a fundamental symmetry and we know that it is violated in theStandard Model (SM), both in the neutrino- and quark-sectors, via mixing. Itis thus natural to expect charged lepton flavour violation (cLFV) but, despitehints of flavour anomalies at g-2 experiment and B factories, it has neverbeen seen in nature and its observation would be unambiguous evidence ofbeyond the SM physics. While stringent limits have been set in the electronand muon channels, the constraints in the tau case are much weaker. Sincenew physics is likely to couple more strongly to the heavier tau, this makes itan ideal place to search. The project will search for LFV tau decays using thefull run-2 and partial run-3 ATLAS data using the golden tau -> 3 muonchannel, with its clean final state. The student will first analyse tau producedin heavy flavour decays, developing methods to estimate the backgroundsand multi-variate techniques to extract the signal. Following this, the workwill be extended to taus produced in W boson decays and the results of thetwo searches combined. Together, these have the potential to providesensitivity beyond the current limit and, if new physics is not observed, setthe most stringent limit on LFV tau decays. The group has previous wideexperience in both W boson measurements and searches in tau final states.